Abstract
Carbon films were prepared on Pyrex by condensation of vapor emitted from an outgassed carbon filament. The reaction vessel was cooled in liquid nitrogen. The BET areas, measured with krypton at 77.8°K, did not vary on subsequent heating in vacuum to 673°K. The area of the films as formed could be varied from 1 to 1000 m2/g. The adsorption isotherms of hydrogen (77.8°K) and oxygen (77.8° and 90°K) were determined. The high-area films reacted with oxygen at temperatures between 373° and 573°sK and in one set of experiments the BET krypton areas did not change during the oxidation study. A fast chemisorption occurred on introduction of the first dose of oxygen. This was followed by much slower rates, the kinetics of which followed the logarithmic rate law and a first-power dependence on pressure. Activation energies varied linearly with uptake for the slow chemisorption, increasing from 16 to 35 kcal as the amount taken up varied from 1 to 6 μmoles of oxygen per film. The first step in the oxidation attack is complex, but the slow step appears to be a reaction between molecular oxygen and surface carbon atoms.
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